The present invention relates to a catheter having transducer which comprises an organic high polymer filmlike piezoelectric element or elements.
With the use of this invention, a filmlike piezoelectric element with excellent pliability can be mounted on a catheter tip, whereby pressure in the living body such as blood pressure, pressure in a thorax, or intrauterine pressure, can be detected directly and read-out as an electronic signal. From the resulting signal wave shapes, a diagnosis can be made.
Also, with this invention the catheter can be provided with two filmlike piezoelectric elements with excellent pliability. These can be mounted on the catheter head and on the catheter side wall, whereby pressure waves at two different points can be detected and read-out as electronic signals corresponding to the pressure waves by the two piezoelectric elements, so that the flow rate of blood can be measured from a time lag between two pressure waves.
In the prior art, for example for measuring pressure in the heart's blood vessel, a catheter connected to an electronic tonometer has been used. A catheter (i.e., a tubule of plastic resin such as fluoride resin, polyurethane, polyethylene, etc.) filled with physiological saline solution is inserted in the blood vessel. Through this catheter the blood pressure existing at the catheter tip is transmitted outside the body, and this pressure is converted into an electronic signal by an electronic tonometer. Wave shapes of this blood pressure are analysed, and from this information, diagnosis is made, and circulation of the blood is analyzed. The foregoing is known prior art.
However, in this prior art method, a real zero point cannot be determined because a difference of water pressure exists between the catheter tip and the transducer (electronic tonometer). Also there are influences such as diminution of pressure, delay of pressure changes due to the visoelasticity of saline, and other physical effects, as the pressure wave at the catheter tip is transmitted to the electronic tonometer through the saline solution. Therefore, accurate measurements cannot be obtained in the above prior art method.
In recent years, a method has become known for solving the above problems, which method is, however, still under study. In this newer and known method, a semiconductor strain gage is mounted on a catheter tip where it will function as a pressure transducer, and the catheter is inserted in the blood vessel or in the living body so that the transducer is placed in the vicinity of the point in the blood vessel or in the body where the pressure measurement is to be made. Measurement is made by the strain gage. Pressure which is applied on this transducer can be converted into electronic signal which is recorded by a recorder.
In this latter method, when the strain gage is used as a pressure transducer, voltage is applied to the strain gage at the catheter tip. Therefore measurement in this method involves the risk that a short-circuit or leak would occur in the human body and inflict an injury upon a person. Furthermore, this latter method has the following defects: the structure of the transducer is intricate, it withstands mechanical impact poorly, and is fragile. Also, clinical application as a catheter is restricted because pliability of the catheter tip is lost by the transducer. Furthermore operation is difficult, because a semiconductor strain gage has a great temperature drift.
The following features are desirable for a transducer to be used in a living body:
(1) that the transducer does not have the above defects; PA1 (2) that sensitivity, stability, and responsiveness are excellent; PA1 (3) that the working range is wide; PA1 (4) that environmental disturbance is small; PA1 (5) that it is easy to insert it into the measured living body and its influence on the living body is minimal; PA1 (6) that it is small-sized; and, PA1 (7) that it is possible to sterilize it.